Backup Database and wordpress website
Before doing anything, backup mysql database and backup entire website. It is important to keep a working copy of your wordpress website before any major changes that may cause your wordpress website not functioning properly, and a complete backup allow you to have a quick rollback to previous working condition for your wordpress website.
If you are familiar with Linux shell commands, you can follow this quick steps :-
SSH login to your hosting account and goto the root folder of your wordpress website.
Enter following command :-
cp -a wordpress_site backup_wordpress_site
where 'wordpress_site' is your working wordpress website folder name, and the 'backup_wordpress_site' is a new folder that will be identical to your working 'wordpress_site' after the copy process. This is a quick way to create a backup of a folder.
Enter the following command to dump out your wordpress mysql database into a text file, this is your wordpress database backup, it contains database schema and data in ascii text format.
mysqldump --database mysql_dbname > dumpfile.sql
Prepare new wordpress files
Login to your wordpress administration screen and deactivate all plugins, this is needed because these plugins may interfere the wordpress core file upgrade process, and there may be compatibility issues of these plugins with the new wordpress core files. Just a reminder again, be sure to double check program update status of each of your wordpress plugins to ensure there is no compatibility issues with the new wordpress core files, you don't want to see important plugins not able to function after the wordpress core upgrade, you may want to decide if you should upgrade wordpress core and deactivate the non-compatible plugins or wait till there is a compatible version of the plugin before upgrading your wordpress website.
After all backups and checks are done, you can start download latest wordpress and extract the compressed files in your hosting account. You can do this with your FTP client or if you are familiar with Linux shell commands, here are the quick steps :-
In your SSH login, enter the following command :-
wget http://wordpress.org/latest.tar.gz (this will download the latest wordpress file to current location, be sure you are at the root folder of your wordpress website)
tar -xzvf latest.tar.gz (extract the compressed file, files will be extracted into a folder named 'wordpress')
mv old_wordpress_folder to backup_wordpress_folder (rename the current wordpress folder to another name to make way for new wordpress files)
mv wordpress to old_wordpress_folder (rename the new wordpress folder to the working wordpress folder name)
copy the following files/folders from 'backup_wordpress_folder' to the current wordpress folder :-
* wp-config.php file
* wp-content folder (except the 'wp-content/cache' and 'wp-content/plugins/widgets' folder)
* wp-images folder
* wp-includes/languages/ (if you are using other languages)
* .htaccess file
Run wordpress upgrade program
After preparing your new wordpress files, you can run the wordpress upgrade program at your browser :-
Follow the instructions on screen and check the status messages when the upgrade program completes, there may be extra steps that require your attention.
Check and update Permalink Structure
After the upgrade process, check your Permalink Structure at administrator panel Options->Permalinks, save and update the Permalink structure and if necessary, save the rules to your .htaccess file accordingly.
Install Plugins and Themes
After getting the wordpress core files to function, you can now work on the plugins, install the plugins as required and be sure to check through the compatibility issues of each plugin.
If you are using a contributed wordpress theme, check the wordpress theme status to ensure it is working for this new wordpress release and if there is any new updates available for this theme, update as required.
After making sure all plugins and theme are installed with the compatible versions, you can reactivate the plugins and switch the wordpress theme to your usual working theme.
Double check your wordpress website
Finally, double check your upgraded wordpress website to ensure everything is working as expected.